Magnetic refrigeration technology has been known for more than twenty years and the advantages it provides with regard to ecology and sustainable development are widely acknowledged. Its limits in terms of its useful calorific output and efficiency are also well known. Consequently, all the research undertaken in this field is focused on improving the performance of such a generator, by adjusting the various parameters, such as the magnetization power, the performance of the magnetocaloric element, the heat exchange surface between the heat transfer fluid and the magnetocaloric elements, and the performance of the heat exchangers, etc.
To that purpose, several types of heat generators with magnetocaloric elements are known, and in particular the magnetocaloric generators comprising a circular structure in which the magnetocaloric elements are arranged in a circle around a central axis and are subjected to a variable magnetic field allowing to create alternately in each of the magnetocaloric elements a heating cycle and a cooling cycle. Such a generator is described in the French patent application no. 07/07612 by the applicant. In this generator, the thermal energy generated by magnetocaloric elements is exchanged with a heat transfer fluid that is forced through the magnetocaloric elements by circulation means. The variation of the magnetic field is obtained by alternating magnetized zones and non magnetized zones, which rotate around the central axis, and are located inside the ring formed by the magnetocaloric elements. They are associated with a field closing device realized in the form of a ring and arranged around the magnetocaloric elements to close or loop the magnetic flux generated by the magnetized zones through the magnetocaloric elements.
The use of such an approximately circular ring is common in the known magnetocaloric generators. It is generally made out of a ferromagnetic material arranged around and in contact or close to the magnetocaloric elements. The ring is made all in one piece. Nonetheless, such a ring shows a certain number of disadvantages.
A first disadvantage relates to the limited ability of this ring to ensure the return of the magnetic field between two magnetized zones. In fact, it consists of a large machined, little structured metallic mass in which the crystalline or metallurgic fibres do not exist or are oriented randomly and do not assist in the achievement of a strong induction in the ring. Furthermore, manufacturing this ring is expensive in terms of material loss.
The second disadvantage inherent to the use of such a ring stems form the fact that it is made of a heat conductive material, which leads to a thermal energy transfer between the ring and the magnetocaloric elements (heat losses) and thus reduces the heat capacity of the heat generator in which it is mounted. The thermal energy produced by the magnetocaloric elements is intended to be exchanged with a heat transfer fluid passing through the latter, and not with the ring achieving the magnetic field return.